> An optimizer that breaks a program is a bad idea. There are> apologists (of program-breaking optimizers) that claim that the> program was already broken without the optimizer, because it does not> conform to some language standard. But actually the program does> conform with the language as it is implemented by the compiler without> optimization and it behaves as intended by the programmer, so it is> correct.

Can you please provide us with the list of optimizations that will not
affect the behavior of any program that uses language features that are
defined by the language standard to have undefined behavior?

Best,
Christopher
[I read an interesting article about the IBM Fortran X compiler, an improved
version of the classic Fortran H compiler. The guy who did it made sure that
the new optimized results were always bit identical to what the old compiler
produced. But I don't know whether he extended that to programs that weren't
valid Fortran, e.g., with aliased arrays. -John]